(a) Field of the Invention
The present invention relates to the technology of air distillation to produce argon by means of an apparatus for air distillation with double column. It concerns first a process of the type in which air to be treated, from which water and CO.sub.2 have been removed and cooled at about its dew point, is injected at the base of the mean pressure column of the double column; a first fraction of rich liquid withdrawn at the bottom of the mean pressure column, is expanded and sent into a head condenser of a column for the production of impure argon connected to the low pressure column of the double column; and a second fraction of rich liquid, withdrawn from the lower portion of the mean pressure column is expanded and injected as reflux into the low pressure column.
(b) Description of Prior Art
To ensure certain productions, for example of argon in liquid form, as well as oxygen and nitrogen, also in liquid form, apparatuses for the treatment of air should be provided with a turbine in which a substantial portion of the flow of input air, for example 15 to 17 % of this flow, or an equivalent flow of mean pressure nitrogen, is expanded.
However, this leads to a deterioration of the conditions of distillation in the low pressure column, which results for example in a decrease of the yield of extraction of argon. A direct withdrawing of mean pressure nitrogen has similar consequences.